1. Field of the Invention
This invention relates to sleeves or belts which are used in paper machines. Such structures of this type, generally, are reinforced through the use of reinforcing fibers which are oriented at an angle turned 45.degree. from the straight machine direction orientation. This arrangement aligns the individual reinforcing strands in the direction of the principal tensile stresses that exist within the sleeve or belt structure as the sleeve or belt is being rotated in the paper machine.
2. Description of the Related Art
Modern "extended nip" or "shoe-type" wet presses used in paper machines generate nip loads on the order of 6000 pounds per linear inch of machine width. These high nip loadings will destroy the belt that forms one side of the nip on a Beloit Extended Nip.RTM. press, or the flexible sleeve that forms one side of the nip on a Voith FlexoNip.RTM. press, Sulzer Escher Wyss Intensa.RTM. press, or Valmet SymPress.RTM. press, if the belt or sleeve enters the nip in a folded or buckled state. Any deformation of the belt or sleeve that reveals local stress and strain necessitates the immediate replacement of the belt or sleeve.
Belts and sleeves, typically, are constructed of urethane or polyurethane material that encases a reinforcement of polyester, Nylon and/or Kevlar.RTM. fibers. The reinforcing fibers may be in the form of woven fabrics or may appear as individual strands of multiple fibers. Individual filaments within a fabric or strand are oriented either parallel to the direction of travel or perpendicular to the direction of travel in the plane of the sleeve surface. These are commonly referred to as machine direction (MD) or the cross machine direction (CMD) on the paper machine, respectively.
The purpose of the fabric reinforcement is to increase the strength of the cover to help it to resist forces that cause local bulging and buckling. While these individual filaments provide support in either the MD or CMD direction, these filaments do not address the problems associated with tensile stresses that are often encountered by the sleeves. Therefore, a more advantageous sleeve or belt would be one that was able to provide the proper strength for the sleeve or belt while at the same time resisting the tensile stresses located within the sleeve or belt.
It is also known, in paper making machines, to employ the use of a wet press felt constructed of a rhombic mesh. Exemplary of such prior art is German Patent No. 1,155,972 to Eduard Kusters. While the Kusters patent teaches the use of a rhombic mesh, the rhombic mesh is used to improve the removal of the water from the paper as the paper is formed upon the press felt. The rhombic mesh more easily allows the water to drain from the paper and the press felt. However, the rhombic nature of the press felt is not utilized to strengthen the press felt. Therefore, a still further advantageous sleeve or belt would be one which utilized a filament orientation which resisted the tensile stresses within the sleeve or belt structure while at the same time providing adequate strength for the sleeve or belt.
It is apparent from the above that there exists a need in the art for a sleeve or belt which is capable of being used in a paper machine, and which at least equals the strength characteristics of the known sleeves or belts, but which at the same time is able to reduce the deformations that occur in response to the tensile stresses within the sleeve or belt and which cause the sleeve or belt to buckle and/or bulge. It is the purpose of this invention to fulfil this and other needs in the art in a manner more apparent to a skilled artisan once given the following disclosure.